Enhanced Thermoelectric Performance of Novel Reaction Condition-Induced Bi₂S₃-Bi Nanocomposites

This is the first report on the enhanced thermoelectric (TE) properties of novel reaction-temperature (T_Re) and duration-induced Bi₂S₃-Bi nanocomposites synthesized using a facile one-step polyol method. They are well characterized as nanorod composites of orthorhombic Bi₂S₃ and rhombohedral Bi phases in which the latter coats the former forming Bi₂S₃-Bi core-shell-like structures along with independent Bi nanoparticles. A very significant observation is the systematic reduction in electrical resistivity ρ with a whopping 7 orders of magnitude (∼10⁷) with just reaction temperature and duration increase, revealing a promising approach for the reduction of ρ of this highly resistive chalcogenide and hence resolving the earlier obstacles for its thermoelectric application potentials in the past few decades. Most astonishingly, a TE power factor at 300 K of the highest Bi content nanocomposite pellet, made at 27 °C using ∼900 MPa pressure, is 3 orders of magnitude greater than that of hot-pressed Bi₂S₃. Its highest ZT at 325 K of 0.006 is over twice of that of similarly prepared CuS or Ag₂S-based nanocomposites. A significantly improved TE performance potential near 300 K is demonstrated for these toxic-free and rare-earth element-free TE nanocomposites, making the present synthesis method as a pioneering approach for developing enhanced thermoelectric properties of Bi₂S₃-based materials without extra sintering steps.